Preparation of dimethyl beryllium

ABSTRACT

A PROCESS OF REACTING ALUMINUM TRIALKYLS OR ALKALI METAL ALUMINUM TETRAALKYLS WITH A BERYLLIUM HALIDE TO FORM A BERYLLIUM DIALKYL, WHICH MAY BE PYROLYZED TO FORM BERYLLIUM HYDRIDE, IS DISCLOSED. BERYLLIUM HYDRIDE IS A FUEL COMPONENT OF SOLID PROPELLANTS AND ALSO A SOURCE OF HYDROGEN AND OF PURE BERYLLIUM METAL.

States Paten 3,812,195 f PREPARATION 0F DIMETHYL BERYLLIUM Roy J. Laran,Greenwell Springs, and Paul Kobetz, Baton Rouge, La., and Robert W.Johnson, Jr'., Savannah, Ga. -assignors to Ethyl Corporation,'Richmond,'Va. No Drawing. Original application Apr. 23, 1965,Ser. No. 451,694.Divided and this application Apr. 26, 1967,

Ser. No. 651,333

. R Int. Cl. C07f 3/00 U. S Il. 260-665 R 1 Claim ABSTRACT OF THEDISCLOSURE A process of reacting aluminum trialkyls or alkali metalaluminum tetraalkyls with a beryllium halide to form a berylliumdialkyl, which may be pyrolyzed to form berylliu'm hydride, isdisclosed. Beryllium hydride is a fuel 'coinponent of solid propellantsand also a source of hydrogen and of pure beryllium metal.

. This is a division of our prior copending application Ser. No. 451,694filed Apr. 23, 1965.

1 This invention relates to a novel process for the preparation ofberyllium hydride. More specifically, it relates to a process wherein aberyllium alkyl is prepared by a novel method and, without separationfrom the reaction system, is pyrolyzed to produce beryllium hydride.

H Beryllium hydride has been synthesized by Coates and 'Glockling [1.Chem. Soc. 1954, 2526] by the pyrolysis of ditertiarybutylberylliumetherate and by Head, Holley and Rabideau [J. Am. Chem. Soc. 79 3687(1957)] using ether-free ditertiary butylberyllium. More recently, asuperior. product has been obtained by the pyrolysis of ditertiary.butylberyllium etherate dissolved in a high-boiling inert-solvent(co-pending application Ser. No. 176,865,

filed Feb. 26, 1962).

An object of this invention is the provision of a novel andimprovedmethod for the preparation of beryllium hy- 'dride Another object ofthis invention is the provision of a method for the preparation ofberyllium hydride which 3,812,195 Patented May 21, 1974 Anotherpreferred embodiment is the use in the first stage of a solvent boilingin the range of from about 50 beryllium alkyl is essentially completebefore it begins to is characterized by simplicity and rapidity ofoperation.

Still another object of this invention is the provision of a method, forthe preparation of beryllium hydride from beryllium halide which doesnot require the isolation of a beryllium alkyl intermediate. Otherobjects .will appear hereinafter.

In accordance with the present invention .it has been found thatberyllium hydride canbe prepared conveniently'andrapidly by means of atwo-stage process without separation, between the stages, ofintermediate reaction products. In the first stage an-organoaluminumcompound, specifically an aluminum trialkyl or an alkali metal aluminumtetraalkyl, wherein the alkali metal has an atomic number of 3 throughand wherein the alkyl group contains from 4-to 10 carbon atoms,inclusive, is caused to react with a beryllium halide to form thecorresponding beryllium dialkyl. In the second stage, the reactionproduct of the first stage is heated Without further treatment todecompose thermally the beryllium dialkyl contained therein to berylliumhydride. The foregoing procedure represents an embodiment of the presentinvention.

Another embodiment of the present invention is the use of a butylaluminum compound in the reaction of the first stage of the process. Apreferred embodiment of the present invention is the use of sodiumaluminum tetra(nbutyl), sodium aluminum tetra(isobutyl), tri n butylaluminum or triisobutyl aluminum in the reaction of the first stage,because when the named compounds are used the reaction of the firststage occurs at a temperature well below that of the thermaldecomposition of the beryllium alkyl intermediate.

decompose thermally. This order of operation is highly desirable if highyield and purity are to be obtained.

The process of the present invention exhibits a number of distinctadvantages over previously known methods for the preparation ofberyllium hydride. Previous methods required the separation of berylliumalkyl from a reaction mixture containing, in addition, aluminum chlorideor excess aluminum alkyl. Since both aluminum and beryllium alkyls arehighly reactive and flammable in air, the separation of the berylliumalkyl from the reaction mixture and its transfer to the pyrolysis vesselwere operations requiring great care in manipulation and the use of aninert atmosphere. These hazardous operations are eliminated by theprocess of the present invention. In addition to improvements in safety,the process of the present invention results in a marked increase in thespeed of operation because of the large saving in time accompanying theelimination of the separation and transfer steps.

The invention will be more fully understood by reference to thefollowing set of illustrative examples in which all parts andpercentages are by weight.

EXAMPLE I A mixture of 10 parts of beryllium chloride bis(diethyletherate) and 24 parts of triisobutyl aluminum was heated at 50 C. for30 minutes; a small amount (25 parts) of diethyl ether was then added.This mixture was then introduced over a period of about 30 minutes intoa highboiling kerosene (Bayol D) maintained at a temperature of about190195 C. After addition was complete, the mixture was cooled andfiltered. The residue on the filter was" washed several times withpentane and dried. Analysis of the product by acid hydrolysis andmeasurement of the evolved hydrogen indicated beryllium hydride of apurity of about 72 percent.

When dodecane or tetralin was used in place of the high boilingkerosene, similar results were obtained.

EXAMPLE II g Sodium aluminum tetraisobutyl (16.7 parts) and 6.8 parts ofberyllium chloride bis-diethyl etherate were combined in 25 parts oftoluene. The sodium chloride precipitated rapidly from the mixedsolutions. The sodium chloride was separated by filtration and waswashed on the filter with successive small portions of toluene andether. White oil parts) was heated to 220 C. and the combined filtrateand washings obtained as indicated above were added slowly to the hotoil. The heating was continued for an additional 10 minutes, after whichthe mixture was cooled and filtered. The beryllium hydride on the filterwas washed with hexane and dried under vacuum. A sample of the productwas analyzed by acid hydrolysis and was shown to contain approximately55 percent of beryllium hydride. v

When the sodium aluminum tetraisobutyl of Example II is replaced bysodium aluminum tetra-n-butyl, similar results are obtained.

EXAMPIJE III Twenty-five parts of triisobutyl aluminum and 4 parts ofpowdered anhydrous beryllium chloride were heated together at 50 C. forone hour. After the addition of 50 parts of benzene, the mixture wasboiled for two hours under reflux. About three quarters of the berylliumchloride reacted. The benzene was removed under vacuum, and the residuewas introduced into Bayol D at 190-200 C. The resulting mixture wasfiltered, and the residue was washed with hexane and dried.-Hydrolyticanalysis indicated beryllium hydride of 70.5 percent purity.

When the triisobutyl aluminum of Example III is replaced by tri-n-butylaluminum, similar results are obtained.

EXAMPLE IV Sodium aluminum tetramethyl (22 parts) and 23 parts ofberyllium chloride bis-diethyl etherate are combined in 50 parts ofether. Sodium chloride precipitates rapidly from the mixed solutions.The sodium chloride is separated by filtration and is Washed on thefilter with successive small portions of ether. The combined filtrateand washings are treated with approximately their own volume of hexane.Dimethylberyllium separates out as colorless needles, which are washedwith a small quantity of hexane and dried.

When the sodium aluminum tetramethyl of Example IV is replaced by thecorresponding potassium, rubidium or cesium compound, similar resultsare obtained.

As indicated above, the original reactants or raw materials employed inthe proces of this invention are an organoaluminum compound and aberyllium halide. The organoaluminum compound employed may be selectedfrom a rather broad range of compounds varying widely in composition.For example they may include trialkyl aluminum compounds and alkalimetal aluminum tetraalkyl compounds. In both series of compounds thenumber of carbon atoms in each alkyl group can vary from 4 to or more.Compounds containing alkyl groups with more than 10 carbon atoms, whileoperable to some extent, are more difiicult to decompose than those withfewer carbon atoms. Examples of the organoaluminum reactants includetri-n-butyl aluminum, tri-isobutyl aluminum, tri-tertiary amyl aluminum,triisohexyl aluminum, tri-n-decyl aluminum, tris(2-ethylhexyl)aluminum,sodium aluminum tetraisobutyl, sodium aluminum tetra-n-butyl, lithiumaluminum, tetra-n-hexyl, potassium aluminum tetraisooctyl, rubidiumaluminum tetradecyl and cesium aluminum tetraheptyl.

The beryllium halide reactants may contain any of the halogens and maybe etherated or unetherated. Examples include beryllium fluoride,beryllium chloride, beryllium bromide, beryllium iodide, berylliumfluoride bis-dimethyl etherate, beryllium chloride bis-diethyl etherate,beryllium bromide bis-di-n-butyl etherate and beryllium iodidebis-diisopropyl etherate. Mixtures of beryllium halide reactants arealso suitable.

In the process of this invention, the ratio of the reactants can bevaried within wide limits, namely, from a 100 percent or greater excess(over the stoichiometric equivalent) of the organoaluminum compound to a100 percent or greater excess of beryllium halide. Normally, anapproximately stoichiometric ratio of the reactant is used.

The reaction temperatures employed in the process of the invention mustobviously be higher in the second stage wherein beryllium alkyl isdecomposed than in the first stage wherein the same compound is formed.In the first stage, therefore, the generally useful temperatures rangefrom about 50 to about 125 C. and in the second stage from about 150 to220 C. Temperatures of from 4 about to about C. and from about C.,respectively, are preferred.

The reaction pressure, for ease in control, is normally aboutatmospheric but pressures ranging from $5 atmosphere or less to 100atmospheres or more may be employed if desired.

The first or beryllium alkyl formation stage" of the process of thepresent invention may be carried out in the absence of a solvent or inthe presence of a lowboiling or a high-boiling aliphatic or aromatichydrocarbon solvent. The second or pyrolysis stage is normally carriedout in a high-boiling aliphatic or aromatic hydrocarbon. The low-boilingsolvents are saturated aliphatic, cycloaliphatic and aromatichydrocarbons boiling, at atmospheric pressure, in the approximate rangeof 80 to C. Examples include 2,3-dimethyl hexane, isooctane,cyclohexane, methylcyclohexane, dimethyl cyclohexane, toluene, xylene,ethyl benzene, propyl benzene, cumene, mesitylene, and mixtures of theforegoing, such as petroleum naphtha, gasoline fractions and kerosene.The high-boiling solvents are saturated aliphatic or aromatichydrocarbons boiling above 170 C. These solvents include n-decane,n-undecane, n-tridecane, n-tetradecane, n-pentadecane, cetane,propylcycloheptane 1,3-dimethylcyclohexane, 1-methyl-2-isoamylcyclohexane, 1,3-dimethyl-S-isobutylcyclohexane, hemimellitene,prehnitene, isodurene, n-butyl benzene, p-cymene, and 1,3,5-triethybenzene, or mixtures of any of the foregoing.

The reactions of this invention may be carried out under any atmosphereinert to both the reactants and products but dry nitrogen is preferred.Other suitable protective atmospheres include hydrogen, carbon monoxide,helium, neon, argon, krypton, and xenon.

The product of this invention is a white to grayish white powder whichhas strong reducing properties. The bulk of the product is insensitiveto water and air, although a small amount of hydrolysis (of the order of10 percent) does occur upon contact with water. When heated in an inertatmosphere, the product is stable up to a temperature of about 160 C.

The beryllium hydride product of this invention is of great value as afuel component of solid propellants. It also represents a convenientsource of small storeabl e quantities of hydrogen and of pure berylliummetal.

I claim:

1. The process for the preparation of dimethyl beryllium which comprisesreacting, in diethyl ether, an alkali metal aluminum tetramethyl whereinthe akali metal has an atomic number from 11 to 55, inclusive, withberyllium chloride, separating the insoluble alkali metal chlorideby-product by filtration, precipitating dimethyl beryllium from thefiltrate by addition of hexane and fieparating and purifying theprecipitated dimethyl beryl- References Cited Everest: The Chemistry ofBeryllium, vol. I, Elsevier Pub. Co., New York, 1964, pp. 91 to 101.

Wood et al.: J. Electrochem. Soc., vol. 104, pp. 29 to 37 (1957).

LELAND A. SEBASTIAN, Primary Examiner U.S. Cl. X.R. 149-109

